* master: (21 commits)
  [GEO] Add WKT Support to GeoBoundingBoxQueryBuilder
  Painless: Add whitelist extensions (elastic#28161)
  Fix daitch_mokotoff phonetic filter to use the dedicated Lucene filter (elastic#28225)
  Avoid doing redundant work when checking for self references. (elastic#26927)
  Fix casts in HotThreads. (elastic#27578)
  Ignore the `-snapshot` suffix when comparing the Lucene version in the build and the docs. (elastic#27927)
  Allow update of `eager_global_ordinals` on `_parent`. (elastic#28014)
  Fix NPE on composite aggregation with sub-aggregations that need scores (elastic#28129)
  `MockTcpTransport` to connect asynchronously (elastic#28203)
  Fix synonym phrase query expansion for cross_fields parsing (elastic#28045)
  Introduce elasticsearch-core jar (elastic#28191)
  elastic#28218: Update the Lucene version for 6.2.0 after backport
  upgrade to lucene 7.2.1 (elastic#28218)
  [Docs] Fix an error in painless-types.asciidoc (elastic#28221)
  Adds metadata to rewritten aggregations (elastic#28185)
  Update version of TaskInfo header serialization after backport
  TEST: Tightens file-based condition in peer-recovery
  Correct backport replica rollback to 6.2 (elastic#28181)
  Backport replica rollback to 6.2 (elastic#28181)
  Rename deleteLocalTranslog to createNewTranslog
  ...

* es/master: (30 commits)
  [Docs] Fix Java Api index administration usage (#28133)
  Fix eclipse build. (#28236)
  Never return null from Strings.tokenizeToStringArray (#28224)
  Fallback to TransportMasterNodeAction for cluster health retries (#28195)
  [Docs] Changes to ingest.asciidoc (#28212)
  TEST: Update logging for testAckedIndexing
  [GEO] Add WKT Support to GeoBoundingBoxQueryBuilder
  Painless: Add whitelist extensions (#28161)
  Fix daitch_mokotoff phonetic filter to use the dedicated Lucene filter (#28225)
  Avoid doing redundant work when checking for self references. (#26927)
  Fix casts in HotThreads. (#27578)
  Ignore the `-snapshot` suffix when comparing the Lucene version in the build and the docs. (#27927)
  Allow update of `eager_global_ordinals` on `_parent`. (#28014)
  Fix NPE on composite aggregation with sub-aggregations that need scores (#28129)
  `MockTcpTransport` to connect asynchronously (#28203)
  Fix synonym phrase query expansion for cross_fields parsing (#28045)
  Introduce elasticsearch-core jar (#28191)
  #28218: Update the Lucene version for 6.2.0 after backport
  upgrade to lucene 7.2.1 (#28218)
  [Docs] Fix an error in painless-types.asciidoc (#28221)
  ...

The method `initiateChannel` on `TcpTransport` is explicit in that
channels can be connect asynchronously. All production implementations
do connect asynchronously. Only the blocking `MockTcpTransport`
connects in a synchronous manner. This avoids testing some of the
blocking code in `TcpTransport` that waits on connections to complete.
Additionally, it requires a more extensive method signature than
required for other transports.

This commit modifies the `MockTcpTransport` to make these connections
asynchronously on a different thread. Additionally, it simplifies that
`initiateChannel` method signature.

The method initiateChannel on TcpTransport is explicit in that
channels can be connect asynchronously. All production implementations
do connect asynchronously. Only the blocking MockTcpTransport
connects in a synchronous manner. This avoids testing some of the
blocking code in TcpTransport that waits on connections to complete.
Additionally, it requires a more extensive method signature than
required for other transports.

This commit modifies the MockTcpTransport to make these connections
asynchronously on a different thread. Additionally, it simplifies that
initiateChannel method signature.